This invention relates, in general, to comparators, and more particularly, to a comparator for enabling a switch that provides either a power supply voltage or a battery voltage.
Many circuits require a battery backup to provide power when a power supply voltage cannot be provided. Power from either a battery or a power supply is coupled through a switch to a circuit. The switch is controlled by a comparator that compares the battery voltage against the power supply voltage. The comparator provides a logic signal to the switch that decouples the power supply from the circuit and couples the battery to the circuit when the power supply voltage is less than the battery voltage.
In general, battery backup is critical for insuring that data is not lost or an orderly shutdown of the circuitry occurs after power is removed. Coupling the inputs of a comparator to a power supply voltage may severely degrade comparator performance. The input voltage to the comparator affects internal voltages of the comparator which can reduce gain or in the extreme case cause the comparator to be non-functional. A comparator used to control a switch must be capable of operating under these extreme input conditions due to the critical nature of its function.
It would be of great benefit if a comparator could be provided having inputs that can be coupled to a power supply voltage without degradation in performance.